Since you are home and have the upper off, it should be no problem.
When you were at the range, you hold the rifle by the handguard with your weak hand, hold the charging handle with your strong hand. With the muzzle pointing down range and being ever watchful of the muzzle, you slam the butt into the ground while pulling back on the charging handle.

How many rounds are you loading in a
magazine ? If you are putting 30 rounds in a mag this could be part of your problem .
I have a bushmaster m4 and if I put 30 rounds in a mag it will double feed on the first or second shot sometimes causeing a jam .this happens with high quality mags as well as low quality mags .
If you continue to have this problem try loading 28 rounds per mag. This should make a difference , it did for me.

well, i've been in the infantry for 11 years now and i would say it was probably the magazine was loaded to 30 rounds . we mostly load to 28 or 27 its choice the mag itself could be bad.
2. yes clean your rifle very good before shooting both before and after shooting.
pay attention to your bolt face and your chamber.
3 is this a new rifle ? check your bolt face often paying close attention to your extractor
i think it was the magazine but you never know
if it is the mag try loading it with less rounds if that doesn't work get a mag repair kit and replace the spring and follower. you can instant message me if you have any more questions i will be at church today till this afternoon so it may be this evening before i can post a reply.
thanks
john